Supramolecular Cd(II) complexes with (E)-N, N′-bis(2-pyridyl) iminoisoindoline (2-pyimiso): Synthesis, X-ray structures, hirshfeld surface analyses, and DFT study of [CdX2(2-pyimiso)2] (X = Cl or NCS)

Article abstract of DOI:10.1080/00958972.2016.1230204

The paucity of coordination entities bearing (E)-N,N′-bis(heteroaryl)iminoisoindolines has prompted us to investigate coordination modes and supramolecular features of (E)-N,N′-bis(2-pyridyl)iminoisoindoline (2-pyimiso), a versatile iminobis(pyridyl) ligand. In this article we report the synthesis, spectroscopic characterization and crystal structure analysis of two Cd(II): 2-pyimiso (1?:2) bis-adducts, [CdX₂(2-pyimiso)2] [X = Cl (1) or NCS (2)]. Our X-ray structural results reveal that 1 exhibits distorted tetrahedral coordination (four-coordinate geometry index τ₄ = 0.92), whereas 2 displays six-coordinate Cd(II) and two four-membered chelate rings (bite angles = 52.5°), each comprising one Cd–N_py [2.247(2) ?] bond and one Cd?N_imine [2.809(21) ?] secondary interaction. Remarkably, in 2 each 2-pyimiso unit binds to Cd(II) according to an unusual bidentate coordination. The contributions of the Cd–N and Cd–Cl bond valences to the total metal valence for both 1 and 2 have been evaluated to confirm the coordination modes of 2-pyimiso, which can be interpreted in terms of J?rgensen’s principle of symbiosis. X-ray structure and Hirshfeld surface analyses have shown that the crystal structure of 1 is determined by two perpendicular 1-D chains formed by weak hydrogen bonds along the a- and c-axes, whereas the supramolecular architecture of 2 exhibits 2-D sheets parallel to the ab-plane interconnected by C–H?πinteractions along the c-axis. A vibrational analysis of both products has been conducted at the DFT B3LYP-D3/LACV3P** level of calculation.

Full text of DOI:10.1080/00958972.2016.1230204

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Supramolecular Cd(II) complexes with (E)-N,N’-
bis(2-pyridyl)iminoisoindoline (2-pyimiso):
synthesis, X-ray structures, Hirshfeld surface
analyses, and DFT study of [CdX (2-pyimiso) ] (X =
2
2
Cl or NCS)
Rodrigo S. Bitzer, Lorenzo C. Visentin, Marco A. C. Nascimento & Carlos A. L.
Filgueiras
To cite this article: Rodrigo S. Bitzer, Lorenzo C. Visentin, Marco A. C. Nascimento
&
Carlos A. L. Filgueiras (2016): Supramolecular Cd(II) complexes with (E)-N,N’-bis(2-
pyridyl)iminoisoindoline (2-pyimiso): synthesis, X-ray structures, Hirshfeld surface analyses,
and DFT study of [CdX (2-pyimiso) ] (X = Cl or NCS), Journal of Coordination Chemistry, DOI:
2
2
10.1080/00958972.2016.1230204
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Date: 30 August 2016, At: 07:41

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://dx.doi.org/10.1080/00958972.2016.1230204
Supramolecular Cd(II) complexes with (E)-N,N'-bis(2-
pyridyl)iminoisoindoline (2-pyimiso): synthesis, X-ray structures, Hirshfeld
surface analyses, and DFT study of [CdX (2-pyimiso) ] (X = Cl or NCS)†
2
2
a
a,‡
a
Rodrigo S. Bitzer , Lorenzo C. Visentin , Marco A. C. Nascimento , and
a,b,
Carlos A. L. Filgueiras
*
a
Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro – RJ, 21941-909,
Brazil
b
Departamento de Química, Universidade Federal de Minas Gerais, Belo Horizonte – MG, 31270-
01, Brazil
9
E-mail addresses:
rodrigobitzer@gmail.com (RSB)
lorenzo.visentin@nanobusiness.com.br (LCV)
chaer01@gmail.com (MACN)
†
1
Supplemental online material: additional figures and DFT optimized Cartesian coordinates. CCDC
421280 and 1422897 contain the supplementary crystallographic data for this paper. These data can be
obtained
www.ccdc.cam.ac.uk/data_request/cif.
Present address. Nanobusiness Informação e Inovação Ltda, Incubadora de Projetos, Instituto Nacional de
Metrologia, Qualidade e Tecnologia, Duque de Caxias – RJ, 25250-020, Brazil.
free
of
charge
from
The
Cambridge
Crystallographic
Data
Centre
via
‡

2
calfilgueiras@gmail.com (CALF)
This work was supported by the Brazilian funding agencies CAPES, CNPq, FAPERJ
and FUJB.
Journal of Coordination Chemistry - Full Paper
*
Corresponding author. Tel.: +55 31 34095758; Fax: +55 31 34095700; E-mail address:
calfilgueiras@gmail.com (C.A.L. Filgueiras).

3
Abstract
The paucity of coordination entities bearing (E)-N,N'-
bis(heteroaryl)iminoisoindolines has prompted us to investigate coordination modes and
supramolecular features of (E)-N,N'-bis(2-pyridyl)iminoisoindoline (2-pyimiso), a versatile
iminobis(pyridyl) ligand. In this article we report the synthesis, spectroscopic
characterization and crystal structure analysis of two Cd(II) : 2-pyimiso (1 : 2) bis-adducts,
2 2
[CdX (2-pyimiso) ] [X = Cl (1) or NCS (2)]. Our X-ray structural results reveal that 1
exhibits distorted tetrahedral coordination (four-coordinate geometry index τ = 0.92),
4
whereas 2 displays six-coordinate Cd(II) and two four-membered chelate rings (bite angles
o
=
52.5 ), each comprising one Cd–N [2.247(2) Å] bond and one Cd···N
[2.809(21) Å]
imine
py
secondary interaction. Remarkably, in 2 each 2-pyimiso unit binds to Cd(II) according to an
unusual bidentate coordination. The contributions of the Cd–N and Cd–Cl bond valences to
the total metal valence for both 1 and 2 have been evaluated to confirm the coordination
modes of 2-pyimiso, which can be interpreted in terms of Jørgensen’s principle of
symbiosis. X-ray structure and Hirshfeld surface analyses have shown that the crystal
structure of 1 is determined by two perpendicular 1-D chains formed by weak hydrogen
bonds along the a- and c-axes, whereas the supramolecular architecture of 2 exhibits 2-D
sheets parallel to the ab-plane interconnected by C–H···π interactions along the c-axis. A
vibrational analysis of both products has been conducted at the DFT B3LYP-D3/LACV3P**
level of calculation.
Keywords: Cadmium; Iminoisoindoline; Coordination modes; Hydrogen bonds; Density
functional calculations.

4
1
Introduction
A survey of the chemical literature reveals that Cd(II) coordination architectures
supported by pyridyl-containing ligands are ubiquitous. X-ray structure analyses of mono,
oligo and μ-(pseudo)halogenido polynuclear Cd(II)–pyridyl complexes have contributed to
our knowledge about bonding and geometry of coordination compounds [1–10] and have
also disclosed supramolecular synthons for engineering of luminescent molecular crystals
[
3b, 3c, 4, 5, 9, 10]. Furthermore, an ever-increasing number of coordination polymers
bearing Cd(II) nodes and pyridyl-containing linkers, including functional metal-organic
frameworks (MOFs), have been reported [11–17]. In this work, we focus on coordination of
E)-N,N'-bis(2-pyridyl)iminoisoindoline (2-pyimiso) (Figure 1) to Cd(II). Cadmium is a
(
1
0
highly-toxic heavy metal [18]. Nevertheless, the closed-shell 4d configuration of its
divalent cation is associated with a diversity of coordination geometries, ranging from linear
through pentagonal pyramidal and bipyramidal to dodecahedral [1]. Thus, Cd(II) reagents,
such as CdX (X = Cl, NCS or OAc) and Cd(NO ) , can be used to investigate the
2
3 2
coordinating ability of new ligands. The heterocyclic compound 2-pyimiso is a scarcely
studied iminobis(pyridyl) ligand with three potentially coordinating nitrogens (Figure 1).
Rotation about the N–pyridyl linkages results in different coordination modes for 2-pyimiso,
as shown in Figure 1.
Figure 1

5
Symmetrically N,N'-disubstituted 1-iminoisoindolines have been known for more
than a century [19]. Nonetheless, only a little more than a dozen examples of (E)-N,N'-
bis(heteroaryl)iminoisoindolines are in the literature [20–30]. Some of them exhibit
antiproliferative activity against cancer cell lines as well as DNA binding properties [26,
27]. In terms of coordination chemistry, little attention has been drawn to the coordinating
abilities of (E)-N,N'-bis(heteroaryl)iminoisoindolines, although they can be polydentate
ligands (Figure 1). To date, only four articles dealing with the coordination chemistry of
(E)-N,N'-bis(heteroaryl)iminoisoindolines have been published, showing that this research
field is still in its infancy [21, 23, 25, 30].
In 2005, Mulyana et al. reported crystal structures of two porous coordination
frameworks containing (E)-N,N'-bis(4-pyridyl)iminoisoindoline (4-pyimiso) as an angular
bis-monodentate linker [21]. [Cd(EtOH)(NO ) (4-pyimiso)] exhibits seven-coordinate
3
2
n
Cd(II) and forms 1-D chains parallel to the crystallographic c-axis, while [Fe(NCS) (4-
2
pyimiso) ] results in 2-D rhombic grids parallel to the ab-plane with six-coordinate Fe(II)
2
n
[
21]. In 2007, Zhu et al. described the crystal structure of the first complex bearing (E)-N,N'-
bis(3-pyridyl)iminoisoindoline (3-pyimiso), [{Cd(ClO )(H O)} (μ-3-
pyimiso) ](ClO ) ·2MeOH [23]. In this dinuclear architecture, each metal ion displays
4
2
2
4
4 2
distorted octahedral geometry and each 3-pyimiso is a bis-monodentate ligand [23]. More
recently, Deng et al. investigated the reaction of AgNO with 2-pyimiso yielding an
3
Ag {(Z)-2-pyimiso} cage-like moiety [25]. We have described the preparation and
3
2
spectroscopic characterization of the first complex containing 2-pyimiso as monodentate-A
ligand, namely trans-[PtCl (DMSO)(2-pyimiso)] [30].
2

6
Other types of N,N'-disubstituted 1-iminoisoindolines have also been exploited as
ligands in coordination chemistry [31–34]. Chitanda et al. described the synthesis of mono
and dinuclear palladacycles containing N,N'-aryl-disubstituted 1-iminoisoindolines as
bidentate monoanionic [C,N] ligands [31–33]. Some of these dinuclear palladacycles were
tested as precatalysts in Heck and Suzuki coupling reactions [31, 33]. Finally, Zabierowski
et al., investigated (E)-N,N'-bis(2-picolyl)iminoisoindoline (pap) as a N,N,N-pincer ligand
[34], reporting the crystal structures of Co(II)- and Cu(II)-pap coordination architectures
exhibiting both five- and seven-membered chelate rings [34].
Because of the scarcity of coordination compounds bearing (E)-N,N'-
bis(heteroaryl)iminoisoindolines, we have undertaken a study of the coordination modes and
supramolecular behavior of 2-pyimiso, a highly-versatile iminobis(pyridyl) ligand (Figure
1
) [25, 29, 30]. The relative orientation of the coordination vectors of 2-pyimiso suggests,
three monodentate and two bidentate coordination modes (Figure 1). In fact, N,N-bidentate
modes are not supported by 3-pyimiso and 4-pyimiso [21, 23]. Herein we report the
synthesis, spectroscopic characterization, including DFT vibrational analysis, and molecular
2
and crystal structure analyses of two Cd(II) : 2-pyimiso (1 : 2) bis-adducts, [CdX (2-
pyimiso) ] (X = Cl or NCS). Hirshfeld surfaces have been analyzed to describe the
2
intermolecular contacts responsible for the crystal structures of both products. Our X-ray
structural results reveal that [CdCl (2-pyimiso) ] (1) exhibits four-coordinate Cd(II) and 2-
2
2
pyimiso as monodentate-A ligand, whereas in [Cd(NCS) (2-pyimiso) ] (2) the metal center
2
2
is six-coordinate and each 2-pyimiso is a bidentate-A ligand. In effect, the increase in the
cadmium coordination number (from four to six) on going from 1 to 2 can be interpreted in
terms of Jørgensen’s principle of symbiosis [35].

7
2
Computational and experimental details
.1 General details
Unless otherwise stated, reagent grade solvents and starting materials were
2
purchased from commercial sources and used as received, or purified according to standard
procedures. Dimethyl sulfoxide-d and methanol-d (Cambridge Isotope Laboratories, Inc.)
6
4
were degassed and stored over 3 Å molecular sieves prior to use. Cd(NCS) was obtained
2
from CdCl and KSCN in EtOH and spectroscopically characterized. 2-Pyimiso was
2
prepared and identified according to the literature [26, 29]. Melting points (M.p.) were
determined using glass capillary tubes in a Mel-Temp II (Lab. Devices, Inc.) apparatus.
Elemental analyses (C, H, and N) were conducted on a PerkinElmer 2400 CHN elemental
analyzer.
2
.2 Spectroscopic measurements
Infrared spectra were recorded on a Magna-IR760 FTIR Nicolet spectrometer. The
–
1
FTIR spectra were obtained using Nujol mulls between CsI windows (4000–200 cm ) and a
–
1
resolution of 4 cm . The FT-Raman spectrum (excitation λ = 1064 nm) of 1 was registered
from a solid sample using a Bruker RFS 100/S spectrometer equipped with Nd:YAG laser
2
and Ge-diode detector cooled at liquid N temperature (77 K). The spectrum was recorded
–
1
up to 8182 spectral accumulations from 3500–100 cm (Stokes portion) with a resolution of
–
1
1
4
cm , and laser power kept at 15 mW to minimize sample degradation. H NMR spectra
were acquired from a Bruker DRX300 instrument operating at 300.13 MHz. All NMR data
were recorded at 293 K, and the chemical shift (δ/ppm) values were determined relative to

8
SiMe
4
6
(δTMS 0.00) with reference to the solvent residual signals, namely δ 2.50 (DMSO-d )
1
1
1
and δ 3.31 (methanol-d ) [36]. Vicinal H– H coupling constants (J) are given in Hz. The H
4
NMR spectra of 2-pyimiso, 1 and 2 are shown in Figure S1.
2
.3 Synthesis of [CdCl (2-pyimiso) ] (1)
2
2
Solid 2-pyimiso (0.211 g, 0.74 mmol) was slowly added to a stirring colorless
solution of CdCl (0.155 g, 0.85 mmol) in MeOH (12 mL), leading to immediate formation
2
of a beige precipitate. The reaction mixture was then stirred and refluxed for 2 h. After
cooling at room temperature, the resulting beige solid (1) was isolated by filtration, washed
with MeOH (4 x 5 mL), and dried under vacuum. The product is only sparingly soluble in
most organic solvents. Single crystals suitable for X-ray diffraction measurements were
obtained by slow evaporation at atmospheric pressure of a dilute solution of 1 in EtOH :
o
DMF (40 : 1). Yield: 0.204 g (0.27 mmol, 73%). M.p.: 251–254 C. Anal. Calcd. for
C H N Cl Cd: C, 57.19; H, 3.73; N, 14.83%. Found: C, 56.48; H, 3.22; N, 14.30%; M,
36
28
8
2
–
1
7
1
1
56. FTIR (Nujol mull between CsI, νmax/cm ): 1645sh, 1637vs, ν(CN)imine; 1609m, 1595s,
586s, 1579sh, 1568m, 1556sh, 1552s, 1483m, 1464vs, 1451sh, 1429vs, 1421sh, 1391s,
385s, 1379s, ν(CC+CN)ring + ρ (HCCH) ; 793m, 777s, 756m, 746m, 740m, 729m, 721m,
r
ring
–
1
s
π(CH); 278s, νas(Cd–Cl); 247m, ν (Cd–Cl). FT-Raman (λ = 1064 nm, νmax/cm ): 282m,
1
ν (Cd–Cl); 252m, ν (Cd–Cl). H NMR (300.1 MHz, DMSO-d , δ/ppm): 5.23 (2 H, s, CH );
as
s
6
2
6
.27–8.84 (12 H, m, heteroaromatic protons).
.4 Synthesis of [Cd(NCS) (2-pyimiso) ] (2)
2
2
2
A mixture of Cd(NCS) (0.156 g, 0.68 mmol) and 2-pyimiso (0.083 g, 0.29 mmol) in
2
MeOH (10 mL) was stirred at room temperature for 48 h, yielding a yellow precipitate.

9
After this period, the solvent was evaporated to dryness, and the resulting solid residue was
washed with cold MeOH (3 x 3 mL) and dried under vacuum. The yellow product (2) is
soluble in most organic solvents. Single crystals suitable for X-ray diffraction measurements
were obtained by slow evaporation at atmospheric pressure of a dilute solution of 2 in EtOH.
2
exhibits C molecular symmetry in the solid state (see Sections 3.2 and 3.3). Yield: 0.060
2
o
g (0.075 mmol, 52%). M.p.: 224–226 C. Anal. Calcd. for C H N S Cd: C, 56.96; H, 3.52;
3
8
28 10 2
N, 17.49%. Found: C, 57.39; H, 3.52; N, 17.99%; M, 801. FTIR (Nujol mull between CsI,
–
1
ν
max/cm ): 2063sh, ν
s
(CN)NCS; 2056vs, νas(CN)NCS; 1618s, ν
s
(CN)imine; 1612sh, νas(CN)imine
;
1
597s, 1581s, 1572sh, 1549vs, 1539sh, 1483m, 1439sh, 1431vs, 1398s, 1379sh,
ν(CC+CN)ring + ρ (HCCH) ; 816vw, ν(CS)NCS; 797m, 783m, 773m, 758w, 728m, π(CH);
r
ring
4
2
6
82m, ρ (CN–Cd–NC) + ρ (CN–Cd–NC); 471s, δ(CN–Cd–NC) + ρ (CN–Cd–NC);
w t r
1
54m,br, ν (Cd–N ). H NMR (300.1 MHz, methanol-d , δ/ppm): 5.25 (2 H, s, CH );
s
NCS
4
2
.42–8.84 (12 H, m, heteroaromatic protons).
.5 Single-crystal X-ray diffraction
X-ray diffraction data for 1 and 2 were acquired at 293(2) K using an Enraf-Nonius
2
KappaCCD diffractometer and graphite-monochromated Mo Kα radiation (λ = 0.71073 Å).
Data were collected with COLLECT [37]. Cell parameters were obtained and refined with
PHICHI [38] and DIRAX [39]. Intensities were submitted to Lp (Lorentz-polarization)
correction (data reduction) using EVALCCD [40] and semi-empirical absorption correction
(multi-scan [41]) using SADABS [42]. The structures were solved by either Direct Methods
(1) or Patterson methods (2) using SHELXS-97 [43]. All atoms except hydrogen were
2
anisotropically refined by full-matrix least squares on F using SHELXL-97 [43]. Hydrogens
3
2
bound to sp carbon (methylene group) and sp carbon (heteroaromatic groups) were

1
0
3
2
geometrically positioned (bond lengths: C(sp )–H = 0.97 Å; C(sp )–H = 0.93 Å) and refined
as riding on their respective carbons with Uiso(H) = 1.2 Ueq(C). WinGX [44] was used as
graphical interface for structure solution and refinement. Crystal structures were analyzed
with PLATON [45] and Mercury [46]. Material for publication, including CIF files and
molecular graphics, was prepared using Mercury [46], enCIFer [47], and publCIF [48].
Crystal data and structure refinement parameters for 1 and 2 are summarized in Table 1.
Table 1
2
.6 Hirshfeld surface analysis
Hirshfeld surfaces [49–54] were constructed from the CIF files to dissect the crystal
structures of both products into non-covalent interactions as well as supramolecular
synthons. Very high resolution molecular Hirshfeld surfaces for 1 and 2 were generated
using CrystalExplorer 3.1 [55], and functions of curvature and distance were mapped onto
the surfaces, including shape index and dnorm [51–53]. Shape index (S) is a dimensionless
surface property defined in terms of the two principal curvatures of the surface and can be
used to distinguish complementary hollows (S = –1.0; concave region; red) and bumps (S =
+
1.0; convex region; blue) where two molecular Hirshfeld surfaces come into contact [51,
5
3]. In particular, adjacent red/orange and blue triangle-like patches on a shape index map
give information about π-π stacking contacts. The function dnorm is a normalized distance
property defined in terms of d (distance from a point on the Hirshfeld surface to the nearest
internal nucleus), d (distance from a point on the Hirshfeld surface to the nearest external
i
e

1
1
vdW
vdW
vdW
i
vdW
nucleus), and van der Waals radii (ri
and re ): dnorm = [(d – r
)/ri ] + [(d –
i
e
vdW
vdW
r
e
)/r
e
] [52, 53]. In this case, red (d
i
–d
e
distances shorter than the sum of vdW radii)
through white to blue (d
information about relevant non-covalent interactions [52, 53]. 2-D fingerprint (d
and 2 were used to evaluate individual intermolecular contributions to the crystal
i
–d
e
distances longer than the sum of vdW radii) patches give us
i
,d
e
) plots of
1
structures [50, 52, 53].
.7 DFT calculations
All calculations were carried out using JAGUAR 7.9 [56] with an energy convergence
2
–
8
criterion of 1.00 x 10 Hartree. Gas-phase geometry optimizations were performed at the
DFT level of theory using either B3LYP [57] or M06-2X [58] hybrid functionals along with
the LACV3P** (6-311G** for non-metallic elements and Los Alamos ab initio ECP [59],
which incorporates the mass-velocity and Darwin relativistic effects, plus valence triple-zeta
basis set for Cd) basis set. The double-zeta LACVP basis set was uncontracted to generate
the triple-zeta LACV3P basis set [60]. D3 dispersion energy correction and its gradients
were computed in every optimization step. The molecular structures of 1 and 2 in the
crystalline state were used as input geometries. No symmetry or geometry constraints were
imposed during the calculations. According to our calculations, 2 also exhibits C molecular
2
symmetry in the gas phase. The vibrational frequencies of each optimized geometry were
computed from analytic second derivatives at the same levels of calculation and verified to
be real. No scaling factors were used to correct the calculated vibrational frequencies. A
comparison between experimental (FTIR and FT-Raman) and calculated (B3LYP-
D3/LACV3P**) frequencies was conducted in order to assign the bands observed in the
vibrational spectra of 1 and 2.

1
2
3
Results and discussion
3
.1 Synthesis and spectroscopic characterization of 1 and 2
2
The 1 : 2 reactions between CdX (X = Cl or NCS) and 2-pyimiso in MeOH led to
formation of two Cd(II) : 2-pyimiso (1 : 2) bis-adducts in moderate yields, 73% for 1 and
2% for 2. According to our preliminary characterization (M.p. and microanalysis), 1 and 2
5
were isolated as analytically pure solids. An excess of CdX (X = Cl or NCS) was used in
2
both reactions in order to promote formation of either oligo or polynuclear species, similar
to many examples in the literature involving Cd(II) halides or pseudohalides and pyridyl-
donor ligands [2–4, 6, 8, 10, 61, 62]. However, even in large excess of the Cd(II) salts only
discrete mononuclear complexes (1 and 2) were isolated from our reactions, as confirmed by
single-crystal X-ray diffraction (see Section 3.2). These observations indicate that bulky 2-
pyimiso prevents oligo and polymerization. Complexes 1 and 2 were also obtained in similar
yields when the 1 : 2 [Cd(II) : 2-pyimiso] stoichiometric ratio (no excess) was used in the
synthetic procedures.
Selected FTIR bands for 2-pyimiso, 1, 2, and related Cd(II) complexes are listed in
Table 2, which shows that the FTIR spectrum of 1 displays two ν(CN)imine bands at 1645
–
1
and 1637 cm , consistent with the presence of two 2-pyimiso units per complex. Two
ν(CN)imine bands were also identified in the FTIR spectrum of 2 (Table 2). In this case, since
–
1
2
exhibits overall C molecular symmetry, the vibration at 1618 cm is ascribed to
2
–
1
νs(CN)imine (A species), while the band at 1612 cm is due to ν (CN)
(B species). The
as
imine
–
1
two ν(CN)imine vibrations of 2 are shifted to lower wavenumbers (Δνmax = –26 and –32 cm )
–
1
as compared to that of free 2-pyimiso (1644 cm ) (Table 2). According to the literature [29,

1
3
3
1, 33], this vibrational red shift is consistent with (semi)coordination of the imine N to
Cd(II) in 2. The ν(CC+CN)ring + ρ (HCCH)ring and π(CH) vibrations of 1 and 2 suggest
r
complexation of only one pyridyl group of 2-pyimiso (Table 2) [29, 30].
Table 2
–
As an ambidentate ligand, thiocyanate, SCN , binds to a metal either via N or S, in
addition to acting as bridging N,S-donor ligand. In general, N-bonded thiocyanate
–
1
complexes exhibit CN stretching frequencies, ν(CN)NCS, near 2050 cm , whereas in S-
bonded thiocyanate complexes these normal vibrations occur at wavenumbers near 2100
–
1
cm [63]. Oligo and polynuclear complexes bearing bridging N,S-bonded thiocyanate
–
1
usually display ν(CN)NCS vibrations near or above 2100 cm [4, 62, 63]. As shown in Table
–
1
2
, the symmetric and asymmetric ν(CN)NCS bands of 2 lie at 2063 and 2056 cm ,
respectively, suggesting a mononuclear N-bonded thiocyanate complex, which is confirmed
by single-crystal X-ray diffraction (see Section 3.2.1). Table 2 also shows that the ν(Cd–Cl)
–
1
–1
bands of 1 lie at 278 (asymmetric) and 247 cm (symmetric), about 100 cm higher than
the Cd–Cl stretch observed in polymeric [CdCl (py) ] , which contains bridging chloride
2
2 n
–
1
and six-coordinate Cd(II) [2a, 61]. For 2, the ν(CS)NCS mode appears at 816 cm as a very
weak band, which is also consistent with N-bonded thiocyanate complex [63]. Bands at 482
–
1
and 471 cm are assigned to ρ (CN–Cd–NC) + ρ (CN–Cd–NC) and δ(CN–Cd–NC) +
w
t
–
1
ρr(CN–Cd–NC) vibrations, respectively. The symmetric Cd–NNCS stretch occurs at 254 cm
Table 2). A more detailed vibrational analysis of both products in the low-frequency region
(

1
4
–
1
(
below 600 cm ) is discussed in Section 3.3. The assignment of bands was confirmed by
DFT calculations in remarkable agreement, as shown in that Section.
1
The H NMR spectrum of 1 displays a sharp singlet at δ 5.23 assigned to methylene
protons (Figure S1). This indicates that in DMSO-d the methylene resonances of 1 are
6
coincident and practically unshifted relative to free 2-pyimiso (δ 5.24 in acetone-d ) (Figure
6
S1). A similar result was observed for 2 in methanol-d (Figure S1). In this product, a sharp
4
singlet at δ 5.25 is ascribed to the methylene protons, showing that they are chemically and
magnetically equivalent on the NMR time scale. As expected, resonances for the
heteroaromatic protons of 1 are at δ 6.27–8.84 and those for the heteroaromatic protons of 2
occur at δ 6.42–8.84 (Figure S1). For free 2-pyimiso in acetone-d
.42–8.98 (Figure S1).
.2 X-ray structure and Hirshfeld surface analyses of 1 and 2
.2.1 Crystal and molecular structures
Product 1 crystallizes in the monoclinic P2 /c (No. 14) space group as a discrete
6
, these signals are at δ
6
3
3
1
mononuclear species (Figures 2 and S2). The molecular structure of 1 in the crystalline state
is depicted in Figure 2. Selected bond lengths and angles for 1 are listed in Table 3.
Figure 2
Table 3

1
5
As illustrated in Figure 2, 1 exhibits a four-coordinate metal center bound to two
chlorides and two nitrogens. In this mononuclear bis-adduct, each 2-pyimiso is coordinated
to Cd(II) through 2-pyridyl attached to the imine N, according to the monodentate-A
coordination (Figures 1 and 2). This coordination was also observed in cis- and trans-
[
PtCl (DMSO)(2-pyimiso)] [30]. Oligo and polynuclear coordination entities have been
2
obtained from reactions between CdCl and pyridyl-containing compounds [2, 6, 10, 61].
2
However, mononuclear adducts [CdX L ] (X = halogen; L = pyridyl-donor; n = 1 or 2) are
2
n
more easily obtained when CdCl is replaced by CdBr or CdI [2, 3, 8, 61]. Indeed, our X-
2
2
2
ray crystallographic results reveal that 1 represents a relatively rare example of mononuclear
bis-adduct of the type [CdCl ] (L = pyridyl-donor ligand) (Figure 2).
2 2
L
The Cd–Cl bond lengths are identical (2.414 Å) and fall within the expected range
for four-coordinate cadmium [64] (Table 3). They are clearly shorter than the Cd–Cl bonds
observed for oligo and polynuclear entities bearing six-coordinate Cd(II) [2, 6, 10, 61, 64].
However, our Cd–Cl bond distances are similar to those reported for [CdCl (6,6'-Me -bpy)],
2
2
which contains four-coordinate Cd(II) [65]. These observations can also be rationalized as
follows: the higher the s character of cadmium the shorter the Cd–Cl bond.
-
In addition to two Cl , the coordination sphere of Cd(II) in 1 contains two N atoms
py
from different ligands (Figure 2). The Cd–N bond distances are: Cd(1)–N(3), 2.415(3) Å
py
and Cd(1)–N(7), 2.177(3) Å (Table 3). The Cd(1)–N(7) bond is more than 0.2 Å shorter
than the Cd(1)–N(3) bond probably because of packing effects, insofar as gas-phase DFT
calculations indicate that they should be very similar (see Section 3.3). Likewise, the Cd(1)–
N(7) bond is shorter and the Cd(1)–N(3) bond is longer than the Cd–N bonds observed in
py
[
Cd(EtOH)(NO ) (4-pyimiso)] [21], [{Cd(ClO )(H O)} (μ-3-pyimiso) ](ClO ) ·2MeOH
3
2
n
4
2
2
4
4 2

1
6
[
23], and [CdCl (6,6'-Me -bpy)] [65]. The Cd···N
distances for 1 are longer than 3 Å
2
2
imine
(Table 3), thus hampering any bonding interaction. The two imine C=N bonds of 1, N(1)-
C(1) and N(5)-C(19), are longer than the respective bond of 2-pyimiso (1.28 Å) [24, 29].
The bond angles obtained for 1 (Table 3) indicate that the metal center exhibits
distorted tetrahedral coordination, which can be confirmed by the four-coordinate geometry
o
o
index τ
4
, defined as: τ = [360 – (α + β)]/141 [66], where (α + β) is the sum of the two
4
largest L–Cd–L angles. For 1, τ is equal to 0.92. Actually, the coordination geometry of 1
4
can be regarded as an intermediate between the ideal tetrahedral and trigonal pyramidal
o
shapes. The dihedral angle between the N–Cd–N and Cl–Cd–Cl planes of 1 is 81.89(7) .
As expected, the aromatic and heteroaromatic rings (least-squares planes) of 1
exhibit negligible or small deviations from planarity, as confirmed by the following root
mean square (rms) values: 0.0065 Å for C(3)-C(8); 0.0059 Å for C(21)-C(26); 0.0453 Å for
C(1)-C(8) (isoindoline ring); 0.0214 Å for C(19)-C(26) (isoindoline ring); 0.0136 Å for
C(9)-N(3) (coordinated py ring); 0.0048 Å for C(27)-N(7) (coordinated py ring); 0.0111 Å
for C(14)-N(4) (uncoordinated py ring); and 0.0037 Å for C(32)-N(8) (uncoordinated py
o
ring). The dihedral angle between the C(1)-C(8) and C(9)-N(3) rings is 88.26(8) and
o
between the C(1)-C(8) and C(14)-N(4) rings is 26.14(15) . In turn, the dihedral angle
o
between the C(19)-C(26) and C(27)-N(7) rings is 72.84(10) , and the C(19)-C(26) and
o
C(32)-N(8) rings are almost coplanar (dihedral angle = 5.56(17) ). For each 2-pyimiso unit,
the coordinated pyridine ring and the isoindoline ring are almost perpendicular to each other.
Complex 2 crystallizes in the centrosymmetric monoclinic C2/c (No. 15) space
group as a discrete mononuclear coordination entity containing only terminal Cd–NCS
linkages (Figure 3). All atoms but cadmium occupy general positions in the unit cell of 2.

1
7
Cd ions, exhibit site occupancy factor equal to 0.50 and lie precisely on 2-fold proper
rotation axes (Figure 4). The asymmetric unit of 2 is shown in Figure S3. This product
exhibits overall C
2
molecular symmetry in the crystalline state, as revealed by Figures 3, 4,
and S3. Selected bond lengths and angles for 2 are summarized in Table 4. All bond lengths
fall within the typical ranges [64, 67].
Figure 3
Figure 4
Table 4
2
As illustrated in Figure 3, complex 2 constitutes a mononuclear Cd(NCS) : 2-
pyimiso (1 : 2) bis-adduct. It exhibits two Cd–NNCS [2.220(2) Å] and two Cd–Npy [2.247(2)
Å] bonds (Figure 3 and Table 4). These bond distances are within the ranges observed for
other coordination entities bearing terminal Cd–NNCS and Cd–N bonds [2c, 4]. In addition,
py
the Cd–N bond length for 2 lies between the two Cd–N bond lengths observed for 1
py
py
(
Tables 3 and 4) and is similar to the Cd–N bond distances observed for
py
[
Cd(EtOH)(NO ) (4-pyimiso)] [21].
3
2
n
In 2, the Cd(II) coordination sphere is formed by two NNCS, two N , and two imine
py
N atoms owing to the intramolecular Cd···Nimine [Cd(1)···N(1)] secondary interactions
Figures 3 and S4). The coordination environment of Cd(II) in 2 is highlighted in Figure
(

1
8
S4. Though longer than the sum of the Cd and N covalent radii (2.15 Å) [68], the
Cd(1)···N(1) distances [2.809(21) Å, Table 4] for 2 are significantly shorter than the sum of
their van der Waals radii (3.15 Å) [69] and should not be neglected. Therefore, based upon
the literature [10, 70], we propose a bonding interaction (semi-coordination) between Cd(II)
and each Nimine in 2, leading to a six-coordinate metal center (Figures 3 and S4). In this
respect, 2-pyimiso is attached to Cd(II) according to the bidentate-A coordination mode,
providing four-membered chelate rings (Figures 1, 3, and S4). This coordination mode of 2-
pyimiso has not been described before. Lengthening of the imine C=N bonds upon
formation of 2 [N(1)–C(1), 1.308(2) Å] relative to the respective bond of 2-pyimiso (1.28 Å)
[24, 29] can be regarded as indirect evidence of the Cd···Nimine interactions.
A Cambridge Structural Database (CSD version 5.36) [71] search was undertaken in
order to identify crystal structures exhibiting four-membered chelate rings similar to those of
(Figures 3 and S4). Our search (filter: R factor ≤ 0.1) returned 31 hits. Among them, three
2
structures (CSD entries: ARULEE, LAQFIS, and VAJTEF) display Cd···N contacts longer
than 2.75 Å [70, 72, 73]. In two articles, these secondary interactions were taken into
account in the attribution of the coordination geometry of cadmium [70, 73]. As
aforementioned, in 2 the Cd···Nimine distances are 2.809(21) Å, and we have included such
interactions in the assignment of the coordination geometry of 2.
The contributions of Cd–N and Cd–Cl bond valences (v ) to the total metal valence
ij
(VCd) for 1 and 2 can be evaluated by using the following empirical expressions: VCd = Σvij
and v = exp[(R – d )/(0.37 Å)], in which d stands for i–j bond distance and R stands for
ij
ij
ij
ij
ij
Brese and O’Keeffe’s bond-valence parameter (Table 5) [74]. According to Table 5, the
Cd···Nimine interactions in 1 do not significantly contribute (~4%) to the Cd total valence and

1
9
should be neglected [10]. On the other hand, the sum of the individual Cd···Nimine
contributions for 2 amounts to ~10%, confirming that these secondary interactions should be
taken into consideration in the assignment of the Cd(II) coordination number and geometry
in 2.
Table 5
As shown in Figures 3 and S4, 2 exhibits a pair of constrained four-membered
chelate rings, Cd(1)–N(1)–C(9)–N(3) and Cd(1)–N(1)#1–C(9)#1–N(3)#1 (symmetry code:
o
#
1 –x+1,y,–z+3/2), whose bite angles are 52.5 (Figure S4 and Table 4). If one takes only
NNCS and N into account, the metal center in 2 is four-coordinate in a distorted tetrahedral
py
coordination geometry (τ = 0.77). In this case, the geometry of 2 would be viewed as an
4
intermediate shape between the ideal trigonal pyramidal and seesaw geometries [66].
Nonetheless, the coordination sphere of Cd(II) in 2 is best described by six nitrogens and
provides a highly distorted octahedral environment (Figures 3 and S4). In effect, Table 4
o
shows that the NNCS atoms are cis [N(5)–Cd(1)–N(5)#1, 102.62(12) ] as well as the imine N
o
atoms [N(1)–Cd(1)–N(1)#1, 80.49 ], whereas the N atoms are trans [N(3)#1–Cd(1)–N(3),
py
o
1
44.05(8) ] (symmetry code: #1 –x+1,y,–z+3/2). The distortion from the ideal octahedral
o
geometry can be attributed to the rather small N –Cd···N
bite angles (52.5 ), whose
py
imine
value is consistent with the literature [70, 72, 73].
As previously reported for 1, the aromatic and heteroaromatic rings (least-squares
planes) of 2 also exhibit negligible or small deviations from planarity. The following rms

2
0
deviations were obtained for 2: 0.0089 Å for C(3)-C(8); 0.0414 Å for C(1)-C(8) (isoindoline
ring); 0.0175 Å for C(9)-N(3) (coordinated py ring); 0.0091 Å for C(14)-N(4)
(uncoordinated py ring); and 0.0385 Å for Cd(1)-N(1) (four-membered chelate ring). The
o
o
dihedral angle between C(1)-C(8) and C(9)-N(3) rings is 58.67(6) , about 30 smaller than
the respective dihedral angle for 1. This difference can be accounted for by the semi-
coordination of the imine N atoms to Cd(II) in 2. Moreover, the C(1)-C(8) and C(14)-N(4)
o
rings of 2 are almost coplanar [the dihedral angle is 3.60(14) ].
According to Jørgensen’s principle of symbiosis [35], when a hard species
coordinates to a metal center, it enhances the ability of the metal to bind to more hard
–
species. N-donor thiocyanate is considered a hard base, while Cl has a softer character.
–
– –
Here, we suggest that when Cl is replaced by NCS ( N=C=S) on going from 1 to 2, the N-
donor thiocyanate ligands harden the Cd(II) center resulting in the shortening of the
Cd···Nimine distances and enhancement of the Cd(1)···N(1) bond valence contributions to the
total metal valence (Table 5).
3
.2.2 Intermolecular interactions and supramolecular synthons
The crystal structures of 1 and 2 result from weak interactions (Table 6). These
contacts were identified by either PLATON [45] or Mercury (sum of vdW radii plus 0.1 Å)
[46] and confirmed by Hirshfeld surface analysis [49–54]. Figures 5 and 6 illustrate the
Hirshfeld surfaces mapped with dnorm and shape index for 1 and 2, respectively. Red spots
on dnorm maps indicate significant non-covalent contacts, which are corroborated by
complementary red/orange and blue patches on shape index maps [49–54]. Starting from
this unbiased analysis and based on more relaxed geometric criteria [76–78], we suggest that

2
1
the weak D–H···A interactions listed in Table 6 are attractive and directional rather than
mere van der Waals isotropic contacts.
Table 6
Figure 5
Figure 6
As shown in Table 6, 1 exhibits intramolecular C–H···N, C–H···Cl, and C–H···π
interactions (Figure S5), in addition to π-π stacking contacts (Figure S6). Table 6 also
reveals that the S(6) motif is highly conserved among the intramolecular D-H···A contacts
of 1. As pointed out in the previous section, for 1 the dihedral angle between the C(1)-C(8)
o
and C(14)-N(4) rings is 26.14(15) , and the C(19)-C(26) and C(32)-N(8) rings are almost
o
coplanar [dihedral angle = 5.56(17) ]. Based on Table 6 and Figure S5, we propose that
these two dihedral angles are largely defined by the C(15)–H(15)···N(1) and C(33)–
H(33)···N(5) (C–H···Nimine) interactions, respectively, whose structural pattern is conserved
across complexes bearing 2-pyimiso as a monodentate-A ligand [29, 30]; the crystal
structure of 2-pyimiso also exhibits this S(6) C–H···Nimine motif (D···A, 2.9 Å; D-H···A,
o
1
22 ) [26, 29]. Moreover, the C(33)–H(33)···Cl(2) interaction is also relevant in
determining the relative orientation of the uncoordinated C(32)-N(8) ring, while the C(7)–
H(7)···Cg(2) and C(25)–H(25)···Cg(5) interactions contribute to the orientation of the

2
2
coordinated 2-pyridyl groups in 1 (Table 6 and Figure S5). This S(6) C–H···π pattern was
also observed in the crystal structure of 2-pyimiso [29]. Two intramolecular parallel-
displaced π-π interactions were observed for 1, Cg(2)···Cg(4) (Cg···Cg, 3.951 Å) and
Cg(3)···Cg(5) (Cg···Cg, 4.256 Å) (Table 6 and Figure S6). These interactions were
identified by Hirshfeld surface analysis as adjacent red/orange and blue triangle-like patches
on the shape index map (Figure S6). In an Ag {(Z)-2-pyimiso} cage-like moiety, π-π
3
2
interactions occur at a shorter Cg···Cg interval, namely 3.64–3.81 Å [25]. On the other
hand, the crystal structure of 2-pyimiso shows Cg···Cg distances of 3.86–4.39 Å [24].
The supramolecular arrangement of 1 involves 1-D zigzag chains along the c-axis
(Table 6 and Figure 7a). This network is formed by the C(30)–H(30)···N(4)i and C(4)–
H(4)···Cl(1)ii motifs [symmetry codes: (i) x,½–y,–½+z; (ii) x,½–y,½+z]. Though at the limit
of the vdW radii, the C(30)–H(30)···N(4)i interaction exhibits a high degree of linearity (D-
o
H···A, 165 ) and should not be neglected [77]. On the other hand, the C(4)–H(4)···Cl(1)–
Cdii contact can be clearly identified in the dnorm map for 1 (Figure 5a, label A) in addition
o
to showing a suitable D–H···A angle of 168 (Table 6). In this 1-D zigzag network (Figure
7
a), the C(30)–H(30)···N(4)i contact should also contribute to the dihedral angle between
o
the C(1)-C(8) and C(14)-N(4) rings [26.14(15) ]. Another 1-D network, perpendicular to the
previous one, was observed for 1 (Table 6 and Figure 7b). This chain, which propagates
along the a-axis, is constructed by robust C–H···Cl–Cd motifs and contribute to a trifurcated
scheme for Cl(1) (Figure 7b). Moreover, these C–H···Cl–Cd contacts were readily
translated into red spots on the dnorm map for 1 (Figure 5a, labels B–D).
Figure 7

2
3
Table 6 shows that the C(12) graph set assignment is conserved in different
networks of 1. Two zigzag chains parallel to the [001] direction are interconnected by anti-
parallel π-π stacking interactions along the a-axis involving the uncoordinated 2-pyridyl
rings C(32)-N(8) (Cg···Cg, 4.114 and 4.527 Å) (Table 6 and Figure 7b). Adjacent
red/orange and blue triangle-like patches on the shape index map for 1 were used to
corroborate these π-π interactions (Figure 5b, labels E and F). In 2-pyimiso, two 2-pyridyl
groups attached to the isoindoline N atom stack at a Cg···Cg distance of 3.938 Å [24]. The
2
1
screw axes are parallel to the [010] direction and generate a sinusoidal topology for 1
Figure S7).
As pointed out in Table 6, each motif described for 2 must be counted twice due to
(
the crystal symmetry. In the crystalline state, 2 exhibits non-classical intramolecular C–
H···N and C–H···π interactions (Table 6 and Figure S5). The geometric parameters
associated with the C(15)–H(15)···N(1) and C(7)–H(7)···Cg(2) contacts of 2 are similar to
those obtained for 1 (Table 6). In fact, the C(1)-C(8) and C(14)-N(4) rings of 2 are almost
o
coplanar [the dihedral angle is 3.60(14) ], thus favoring the C(15)–H(15)···N(1) hydrogen
bond. For 2, we also propose an intramolecular C–H···π interaction involving thiocyanate π
electrons as acceptor (D···A, 3.601 Å), rather than the expected N or S acceptors (Table 6
and Figure S5) [79]. Together, the supramolecular data obtained for 1 and 2 reveal that the
S(6) C(15)–H(15)···N(1) and C(7)–H(7)···Cg(2) motifs are robust (Table 6). An
intramolecular π-π stacking interaction involving the isoindoline rings (Cg···Cg, 4.076 Å) is
suggested for 2 and confirmed by Hirshfeld surface analysis (Table 6 and Figure 6b, label
D’). This centroid-centroid distance falls within the typical range for 2-pyimiso [24].

2
4
Complex 2 forms a 2-D network parallel to the ab-plane owing to C–H···N, C–
H···S, and C–H···π non-covalent interactions (Table 6 and Figure 8). This network is
constructed by the C(12)–H(12)···N(4)vii and C(11)–H(11)···S(1)viii [(vii) ½+x,½+y,z;
(viii) ½+x,–½+y,z] contacts along the diagonal of the [110] plane and by the C(4)–
H(4)···C(19)ix [(ix) x,–1+y,z] interaction along the b-axis (Figure 8). This latter motif
involves the thiocyanate π system as acceptor [79], as can be seen in Figure 8. The C(12)–
H(12)···N(4)vii (D···A, 3.562 Å) and C(4)–H(4)···C(19)ix (D···A, 3.878 Å) interactions
occur at the limit of the vdW radii; however, they show a satisfactory degree of linearity
o
o
since the D–H···A angles are 144 and 163 , respectively (Table 6).
Figure 8
Table 6 reveals that the C(9) chain supramolecular assignment is conserved in the 2-
D network of 2. Furthermore, two adjacent sheets of 2 are interconnected along the c-axis by
2
2
C–H···π interactions, which form discrete R
2
(14) and R
2
(18) motifs (Table 6 and Figure
S8). The supramolecular architecture of 2 shows that H(11) is bifurcated. The acceptor
thiocyanate C is also bifurcated, involved in both intra and intermolecular contacts (Table
6
).
As illustrated in Figures 5 and 6, most intermolecular contacts described in Table 6
have been recognized in the Hirshfeld surfaces mapped with dnorm, as red to white spots, and
shape index, as complementary hollows (red/orange) and bumps (blue). Additionally, 2-D
fingerprint (d ,d ) plots for 1 and 2 have been used to identify and evaluate individual non-
i
e

2
5
covalent contributions to the Hirshfeld surfaces (Figure S9) [50, 52, 53]. The H···H
51.6%), H···C/C···H (19.8%), H···Cl/Cl···H (15.8%), and H···N/N···H (7.3%) close
contacts have major contributions to the Hirshfeld surface area for 1. After H···H contact,
(
the H···C/C···H interactions, referred to as C–H···π interactions, dominate. The C···C close
contact, associated with π-π stacking, only contributes 3.2% to the Hirshfeld surface for 1
(Figure S9). The H···H (35.2%), H···C/C···H (24.3%), H···S/S···H (12.8%), and
H···N/N···H (11.1%) close contacts significantly contribute to the Hirshfeld surface area for
the asymmetric unit of 2. This reveals that the H···N/N···H and H···C/C···H (C–H···π
interactions) contacts contribute more to the Hirshfeld surface area for 2 than they contribute
to the surface area for 1; π-π stacking (C···C contact) only contributes 3.8% to the Hirshfeld
surface for 2 (Figure S9).
3
.3 DFT calculations and vibrational analysis of 1 and 2
A gas-phase DFT study of 1 and 2 has been carried out at the B3LYP-
D3/LACV3P** and M06-2X-D3/LACV3P** levels of calculation. D3 dispersion correction
was used in order to obtain a better description of the coordination geometry. Cartesian
coordinates of all optimized geometries are supplied in Tables S1 and S2. Table 7 reveals
that the DFT optimized and X-ray molecular structures are slightly different (overall mean
percent deviations ≤ 5%); but the differences do not compromise a comparative analysis of
4
the calculated and experimental vibrational frequencies. The τ values (0.82 and 0.83)
obtained for 1 from our DFT calculations (Table 7) are consistent with a trigonal pyramidal
coordination environment for Cd(II) in the gas phase [66]. According to our calculations,
which were performed without constraints, 2 also exhibits overall C molecular symmetry in
2
the gas phase (Table 7). The Cd···Nimine distances and the N –Cd–N
bite angles
imine
py

2
6
calculated for 2 resemble the X-ray structure values (Table 7). The structural results
obtained for 1 and 2 do not significantly vary with the DFT functional, as can also be seen in
Table 7.
Table 7.
A vibrational analysis of both products has been conducted at the B3LYP-
D3/LACV3P** level of calculation. No scaling factor was used to correct the calculated
frequencies. Moreover, no imaginary frequencies were found, indicating that the optimized
structures are minima in the potential energy surfaces of 1 and 2. For these products, all
normal modes are both IR and Raman active. Nevertheless, it is important to distinguish the
symmetric (A species) and asymmetric (B species) vibration modes of 2. Our DFT results
support the assignment of bands in Section 3.1. The analysis of the low-frequency region
–
1
(
600–200 cm ) of the vibrational spectra of 1 and 2 is summarized in Table 8.
Table 8
–
1
A number of intraligand bending modes occur from 600–300 cm (Table 8). The
–
1
–1
out-of-plane intraligand bending vibrations at 472 cm (1) and 474 cm (2) remained
unchanged relative to the respective band of 2-pyimiso. Most low-frequency intraligand
bands underwent slight shifts upon complexation. The low-frequency vibrational spectrum
–
1
of 1 shows that the ν (Cd–Cl) and ν (Cd–Cl) bands lie at 278 and 247 cm , respectively.
as
s

2
7
Furthermore, it indicates that the in-plane δ(N –Cd–N ) + ρ (N –Cd–N ) and out-of-
py
py
r
py
py
–
1
w t
plane ρ (Npy–Cd–Npy) + ρ (Npy–Cd–Npy) bending modes occur at 265 and 213 cm ,
r w t
respectively. Similarly, the δ(Npy–Cd–Npy) + ρ (Npy–Cd–Npy) and ρ (Npy–Cd–Npy) + ρ (Npy–
Cd–Npy) bands of 2 lie at the same region (Table 8). This is consistent with similar Cd(II)–
2
-pyimiso coordination environments in both products.
4
Conclusions
The 1:2 reactions between CdX (X = Cl or NCS) and 2-pyimiso in MeOH yielded
2
two Cd(II) : 2-pyimiso (1 : 2) bis-adducts, [CdX (2-pyimiso) ] [X = Cl (1) or NCS (2)].
2
2
These complexes were spectroscopically characterized, and DFT calculations were
performed to support our vibrational analyses. Single-crystal X-ray diffraction studies
revealed that 2-pyimiso adopts different coordination modes in these products. In 1, 2-
pyimiso is monodentate-A mode, whereas in 2 it binds to Cd(II) bidentate-A mode (Figures
and 3). The contributions of the Cd–N and Cd–Cl bond valences to the total cadmium
2
valence in 1 and 2 have been evaluated to confirm the assignment of the coordination modes
of 2-pyimiso, which agree with Jørgensen’s principle of symbiosis. Furthermore, X-ray
structure and Hirshfeld surface analyses have indicated that the crystal structure of 1 exhibits
intramolecular C–H···N, C–H···Cl, and C–H···π interactions, while the crystal structure of
2
shows intramolecular C–H···N and C–H···π contacts. The crystal packing of 1 is
constructed by 1-D networks interconnected by π-π stacking interactions, whereas in 2
crystal topology is dictated by 2-D sheets parallel to the ab–plane interconnected by C–
H···π interactions. Finally, analysis of the structural motifs has revealed a tendency for
conservation of supramolecular synthons across complexes containing 2-pyimiso.

2
8
Comparing 1 with 2, one can see that the intramolecular S(6) assignment is conserved as
well as the intermolecular C(10) pattern. Also, the C(12) motif is conserved in different 1-D
chains of 1, while the C(9) graph-set assignment is well conserved in the crystal structure of
2
.
Supplemental online material
Additional figures and DFT optimized Cartesian coordinates. CCDC 1421280 and
1
422897 contain the supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
The authors are grateful to CAPES, CNPq, FAPERJ, and FUJB for sponsorship, to
LDRX-UFF for the use of X-ray diffraction facilities, and to Prof. J. G. S. Lopes (UFJF) for
the FT-Raman spectrum.

2
9
References
1
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2
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